Compressed gas circuit interrupter



Jan. 12, 1954 w. M. LEEDS ,666,

COMPRESSED GAS CIRCUIT INTERRUPTER Filed Sept. 13, 1949 2 Sheets-Sheet 1 73 1| 7o 72 F|g.2. 43 I 4 34 36 3O 18 23 I2 25 37 1 29 2 0 8 4s 4s 1 47 2 l5 16 3| 4 J 32 I3 so 59 2 g L f6 I s3 62 79 J 1 x 2 T4 68 9 1Q 5 2 l 8| 7s WITNESSES: INVENTOR Winthrop M. Leeds.

. BY za/nama Jan. 12, 1954 w. M. LEEDS ED GAS CIRCUIT INTERRUPTER COMPRESS Filed Sept. 15, 1949 2 Sheets-Sheet 2 as as 7 85 wV/A WETNESSES:

Patented Jan. 12, 1954 UNITED STATES PATENT OFFICE COMPRESSED GAS CIRCUIT INTERRUPTER Application September13, 1949, Serial No. 115,453

12 Claims.

This invention relates to circuit interrupters in general, and more particularly to arc-extinguishing structures for circuit interrupters of the compressed-gas type.

Modern high-voltage circuit interrupters for voltages of 11-5 lav. and above should meet the following requirements:

1. The interrupter should be high speed in operation, with no more than one-twentieth to onetwelfth second from energizing the trip coil to are extinction.

2. The interrupter should b suitable for highspeed reclosing duty, with a time for such reclosing duty within one-fourth to one-third secnd.

3. There should be provided easy inspection and ready maintenance, of the arcing contacts in particular.

4. There should also be provided rapid interruption of transmission-line charging current with minimum restriking.

5. The over-all dimensions of the interrupter and the weight thereof should be moderate and at a minimum.

6. There should be p esent a minimum of inflammable materials such as oil.

It is a general object of my invention to provide an improved circuit interrupter of the compressed-gas type, which will meet all of the abovementioned requirements, and will more closely adhere to an ideal design than other circuit interrupters previously designed for this application.

A more specific object of my invention is to provide an improved circuit interrupter of the compressedas type in which interrupting heads of the orifice type are employed, between which is disposed an improve stationary exhaust chamber for the maintenance of high-dielectric strength during the interrupting operation.

Another object is to provide an improved circuit interrupter of the compressed-gas type having improved stationary inte'rupting heads of the orifice type, the latter being so configured as to provide a multiplicity of axially-aligned orifices to subject the drawn arc to a plurality of oxially-directed gas blasts to bring about its ready extinction.

A further object is to provide a sturdy and igidly constructed compressed-ga circuit inerrupter incorporating the operating advantages eretofcre found only compressed-gas circuit interrupters of the type having movable interrupting heads, but with the further advantage of having an improved exhaust reservoir for highdielectric strength during interruption. with the several component parts rigidly secured together to thereby make the entire circuit interrupter more rigid and sturdy.

A still further object is to provide an improved compressed-gas circuit interrupter in which the assembling operation is more easily carried out.

A more specific object is to provide an improved compressed gas circuit interrupter in which the contact structures may readily be removed for inspection and maintenance without necessitating a disassembly of the other major component parts of the interrupter.

Another object is to provide an improved Circuit interrupter with improved shock-absorbing means during the opening operation, but yet readily adapted for high-speed reclosing operations.

Further objects and advantages will readily become apparent upon reading the following specification taken in conjunction with the drawings, in which:

Figure 1 is a side elevational view of an im proved compressed-gas circuit Lnterrupter embodying my invention and shown in the closedcircuit position;

Fig. 2 is a vertical sectional view through the upper left-hand portion of my improved circuit interrupter, the contacts being shown in the closedcircuit position;

Fig. 3 is an enlarged vertical sectional view through a modified type of interrupting head assembly of the multiple-orifice type, with the contacts being shown in the open-circuit position; and,

Fig. 4 is a vertical cross-sectional view taken through the modified type of interrupting head of Fig. 3 substantially along the line IV-IV, and looking in the direction of the arrows.

Referring to the drawings, and more particu larly to Figure 1 thereof, the reference numeral I designates a base upon which are mounted ceramic insulating columns 2, At the upper ends of insulating columns 2, 3 are fixedly positioned gas-reservoir chambers l, Passing through each reservoir chamber Li, and preferably welded thereto, are stationary metallic tubes 6, 7 having their opposed inner ends threaded, as at 8, t.

lhreadedly secure-:1 to each metallic tube 6, l is an insulating orifice-type interrupting head 56, H. Preferably locking nuts 12 are employee to loci: the interrupting heads 16, l i into position once they are threadedly secured in the proper place on the tubes 6, '1'.

The two interrupting heads, as mentioned, are or the orifice type, each having an orifice opening it, i l passing therethrough. Two movable interrupting contact rods l5, 5, each of hollow con structicn, are movable through the orifice openings id, id.

With particular attention being directed to the left-hand interrupting head iii, as viewed in Figure 2, it will be noted that the hollow rod-shaped contact in is operatively moved by a fluid motor, generally designated by the reference character it, and comprising a pneumatic piston l9 reciprocatingly mounted within an operating cylinder 2@. A compression spring 2! is positioned within the operating cylinder 2e, and has one end thereof seated against the left face of the operating piston l9. lhe left-hand end of spring 2i seats against an apertured stop 22, integrally formed, in this instance, with a shock-absorbing piston cylinder 23. Within the piston cylinder 23 is movable a shock-absorbing piston 24 rigidly secured and movable with a piston rod 25 attached to the pneumatic piston 59.

It will be noted that the opening '25 through the hollow contact rod i leads, as at 2?, to the region 28 back of the pneumatic piston G9, which is vented through apertures 29 to region 343 and hence by means of the apertures 3|, in cap-plate member 32, to the surrounding ambient atmospheric region 33.

A ring of bolts 34 secures a flange portion 35 of the operating cylinder 2b to a stationary ou wardly-extending flange portion 36 of the metallic tube A ring of bolts 3? secures the cap-plate member 32 to the operating cylinder 26. Thus, the entire movable contact assembly, generally designated bv the reference numeral 3%, may be withdrawn toward the left, completely out of the tube ii, upon removal of the bolts 3 from the flange portion 36.

Once the movable contact assembly 38 has been removed from the tube 5 in the foregoing manner, it may easily be taken apart by removing the bolts B to enable the shock-absorbing piston cylinder 23 to be removed from the operating cylinder 23 to thereby permit ready removal of the hollow movable contact rod 55. Thus replacement of the contact rod 55, or inspection of the entire movable contact assembly 38 is readily had without disturbing the interrupting head iii or any other maior component part of the compressed-gas circuit interrupter.

A ball check valve ,6, controlling a vent opening it in back of the shock-absorbing piston 2 1, permits trapping of air back of the shock-absorbing piston is during the opening operation of the contact rod 5 5, but permits rapid rightward closing movement of the contact rod It to permit rapid reclosing of the interrupter should it be desired under the influence of compression spring it. Thus the opening movement of the contact rod i5 is cushioned, but the reclosing movement of the contact rod is is rapid, ball to moving away from the vent opening t! during such closing movement or" the contact rod it. A pin 42 is provided to keep the ball so in proper position.

The left-hand line terminal is secured, to the reservoir chamber i and is designated by the reference character 43. To insure good contacting engagement between the contact rod 15 and the line terminal &3, a pair of helical springs i l, at of good-conducting material, such as phosphorbronze, are provided, encircling the contact rod in and biased by a compression spring it toward the tapered ends 571 of the right-hand end 4 8 of,

4 the operating cylinder Ell. Preferably washers at are interposed between the compression spring and the helical springs 5:3, to insure proper even pressure against the springs st,

With the foregoing arrangement it will be apparent that the helical springs as, 455 insure good contacting electrical engagement between the contact rod l5 and the right-hand end 58 of the operating cylinder 25. Thus the electrical circuit passes by way of contact rod i5, helical springs as, 45 to operating cylinder 2%, thence to bolts E i, flange portion 55, metallic tube 6, reservoir chamber i to left-hand line terninal The construction and operation of the righthand hollow contact ro it be the san e as that heretofore discussed in connection with the left-hand hollow contact rod i5, with the exception that no line terminal is provided the top of the reservoir chamber instead, at the top of a ceramic column 5Q mounted on the base i is provided a movable isolator switch operating assembly 5!, which serves to rotatably move a movable isolator contact 52 to its open and closed-circuit positions, as shown in Fig. l. The right-hand end of the movable isolator contact 52 makes contacting engagement with a pair of jaw-type stationary contacts 53, the latter being mounted at the top of a ceramic or insulating column the latter likewise mounted upon the base i. If desired, a current transformer may be iounted interiorly within the upper end of the ceramic column 56. The right-hand line terminal of the interrupter is designated by the reference character 55 and is disposed at the upper end of the column 54.

If desired, the ceramic column 55 may be rotatably mounted about its vertical axis to thereby mechanically cause the operation of t-. e movable isolator-contact operating assembly at disposed at the top thereof. During such rotatable motion of the ceramic column 5i the movable isolator contact 52 is moved from its closed-circuit position, shown in full lines in Fi ure l, to its opencircuit position, shown by the chain lines at of Figure 1. Normally, this occurs immediately following extinction of the are within the interrupting heads iii, H of the arc-extinguishing unit 5?.

From the foregoing description it will be apparent that in the closed-circuit position of the interrupter, as shown in Figure 1, the electrical circuit passing therethrough includes line terminal 42%, chamber 5, tube 5, operating cylinder 26, springs lie, 35, contact rod 55 to char -ber 5 in like manner, as heretofore discussed, metallic isolating-switch operating assembly bi, movable isolator contact 52, stationary fingers through a current transformer, not shown, but which may be provided within the upper end of the ceramic column 5 3, to the line terminal 55.

The gas pressure within the reservoir chambers i and 5 is at high pressure, say at 200 to 350 pounds per square inch. This gas pressure is brought from a reservoir (not shown) through an insulating conduit 53, associated with each insulating column 2, 3. Likewise a blast valve 59 is associated with each reservoir 5, secured to a stem 68 actuated by a piston 6i movable within an operating cylinder 62. She operating cylinder 62 is provided with a bleeder opening 63, thereby permitting high-pressure gas within the region 64 of the chamber 2 to pass through the bleeder opening 63 to the lower non-Working side 65 of the piston 5!. The piston 61 is biased upwardly to the blast-valve-closed position by a compression spring 65. The region 6?, below the piston 6|, may be vented by the opening of a pilot valve 68, the latter being actuated downwardly, during its opening stroke, by an insulating pilot-valve operating rod 6d. The valve rod 69 may be mechanically connected with the tripping mechanism of the interrupter, the latter, notv shown, being electrically connected with the current transformer heretofore discussed.

Positioned between the two operating heads it, it is an insulating cylindrical member itl having its ends 'il', '52 disposed in recesses i3, 74 provided in the opposed inner corrugated faces of the operatin heads is, H. The cylinder "9 provides a confined exhaust chamber 75, which prevents the free access of interrupting gas pressure to the outside atmosphere 33.

If P is the pressure of the gas on the exhaust side of the orifices it, it, and P1 is the pressure of the gas on the entrance side of the orifices l3, l4, and the gas employed is air, then preferably This means that when the quotient of the exhaust pressure of the orifice divided by the entrance pressure of the orifice equal to or less than 0.53, considering air as the applicable gas, then the compressed air will flow through the orifices l3, i l at acoustic velocity. If the quotient of the exhaust pressure of the orifice divided by the entrance pressure of the orifice varies from .53 to 1.0 the velocity or the compressed air flow through the orifices it, It will correspondingly decrease from acoustic velocity to zero.

This means that even with the back pressure or" the gas provided by the pressure P in the exhaust chamber is at 0.53 es the entrance pressure P1 acoustic-velocity gas flow will still take place through the orifices 13, I l, and yet the dielectric strength of the interrupting region will be greatly increased because of the pressure, as compared to th condition which would result if the gas flow through the orifices it, It were permitted to freely vent to the outside atmosphere An overpressure valve, generally designated by the reference character 5, is provided to open the exhaust chamber upon a predetermined rise in pressure. The overpressure valve 16 includes a valve plate TI, biased to its closed position by a compression spring 18, and provided with a bleeder opening iii to bring the pressure P down fairly rapidly to atmospheric pressure at the end of the interrupting period. If the bleeder opening it were not provided, then the exhaust pressure would be maintained at a relatively high value following the interrupting operation, and this would impede a rapid reclosing operation, since such pressure would act against the reclosing action of the compression spring 25. The overpressure valve it is provided with vent openings 86 to atmosphere, the latter being provided in a cup member 8 l.

The opening operation of the interrupter'will now be described. In response to manual operation of the interrupter, or in response to overload current passing through the interrupter, the valve rods 59 in both columns 2, 3 are moved downwardly. This vents the lower side of the blast-valve pistons 8i to open the blast valves 55 and permits gas under pressure from the regions i l within reservoirs l, 5 to fiOW past the blast valves through one or re ports 82 to the working faces of the pneumatic pistons E5. The

gas pressure forces the pistons is toward their open positions, thereby separating the contacts l5, l6 to draw an arc therebetween. The shockabsorbing piston 24 moves within the shockabsorbing piston cylinder 23 to close the ball check valve 46 against the opening a! and to cushion the final portion of the opening operation of the interrupter. Durin the openin operation the compression spring 22 is compressed, and compressed air flows out through the orifices l3, M in the direction indicated by the arrows to extinguish the ar". Also some air flows through the contact rods l5, E5 to the region in back of the pistons 59 and hence to atmosphere. This how through the contact rods 15, it themselves assists in the extinguishing action at the ends of the arc.

Since the exhaust chamber iii is confined, the dielectric strength of the gas within the inter-- rupting region is increased, and yet, because of the proper ratio between P and Pi, acousticvelocity gas flow is still obtained through the orifices l3, l4. Arc extinction is quickly brought about, and then the ceramic column is rotated to move the disconnect contact 52 to the open position 56, as shown in dotted lines in Figure 1. Following the opening of the disconnect contact, the valve rods 69 are moved to their upward close positions. This permits the high-pressure gas, passing through the bleeder opening to equalize the pressure within the regions 84, 67 to thereby perrnit reclosure o the blast valve 5 3. Because of the provision of the bleeder opening :9 in the overpressure valve it, the pressure P in the exhaust chamber Eli rapidly drops to atinospheric pressure, ther 3y permitting the compr ssion spring 2! to move the pneumatic pistons l9 and reclose the contacts, the ball valve 38 opening during such reclosure. Since the iso lating switch has already opened, no current will flow. Closing of the breaker is accomplished merely by closing the isolator switch, which coinpletes the circuit.

When high-speed reclosing duty is desired, the breaker control is modified so that the isolator switch will not open after the o ening of the arcing contacts and extinction of the are by the compressed-air blast. Under these conditions, reclosing of the arcing contacts, following the closing of the blast valve 59, will actually reestablish the circuit through the breaker. If the overload or fault conditions still exist, a second opening and are extinction in the interrupter heads takes place, the control being arran ed so that this time the isolator switch will open and leave the breaker in the fully-open position.

If desired to increase the rigidity of the interrupting heads II), II, insulating tie bolts 83 may be provided. The position of the air reservoirs 4, 5 and the blast valve 59 at the top of the supporting columns 2, 3 permits high-speed operation, since high gas pressure is immediately available in the interrupting region without the delay which would result if pressure had to be built up in long pipes from a distant reservoir and blast valve. The molded heads 10, H may be formed from hard rubber or similar insulating material, or even'from a ceramic material, although the tougher materials are preferred for higher interrupting capacity breakers. As shown, an -arc resisting and non-tracking orifice lining material may be used at [3 and It such as unfille polytetrafluoroethylene, horn fibre, molded asbestos, or zirconium oxide. As mentioned previously, it is noted that the complete contact and piston assembly may be removable as a unit. For convenience in assembling the molded heads l9, H and tube Hi, forming the exhaust chamber 15, the mounting tubes 5, l on the respective columns 4, may have right and left-hand threads 8, 9. The separate tie bolts 83 may be found necessary to hold. the heads [0, l I together against the pressure P in the exhaust chamber. The tube 58 leading to the reservoir i be made of zirconium.

From the foregoing description it is apparent that I have provided an improved compressedgas circuit interrupter, in which by the positioning of the reservoir chambers l, 5 at the tops of the columns 2, 3 high-speed operation is achieved and high-pressure gas is available quickly with low-pressure drop. The contact assembly is easily removed without disturbing the rest of the interrupter, and the entire construction is rigid and sturdy in arrangement. The use of the fixed exhaust chamber permits high dielectric strength adjacent the arcing region, and yet does not interfere with the maximum velocity attainable of gas flow through the orifices 13, Hi. Following interruption, the exhaust region is rapidly lowered to atmospheric pressure to permit rapid reclosing operations to the achieved.

Where two orifices per pole are insufiicient for the voltage rating, additional orifices may be added effectively, as shown by the modified interrupting head construction disclosed in Figures 3 and 4, without losing the simplicity of a single pair of contacts. Referring to these figures it will be noted that I have provided modified interrupting heads 84, 85 with an intermediately-disposed interrupting head 85, the latter being positioned between two insulating tubes 81, 88 forming exhaust chambers l5. Preferably corrugated ceramic tubes 39 are provided within the exhaust chambers 15 interconnecting conduits 9i 9! within the respetcive interrupting heads 84, 85 with conduits 92 formed within the intermediately positioned interrupting head 86. The intermediate interrupting head 86 provides a central pressure chamber 93, from which the gas fiows outwardly, as indicated by the arrows. If desired, resilient washers 94 may be provided at the ends of the corrugated ceramic tubes 89, to be compressed during assembly of the interrupting heads 8%, 35 and 86 until stopped by the outer insulating tubes 8 88. Tie bolts 95 of insulating material may be provided, as before, to insure strength and rigidity of the assembled interrupting heads.

t will be observed that by use of the intermediately-disposed interrupting head 3% two additional orifices fill are provided. Thus the are 98 is subjected to high-pressure gas flow through a plurality of orifices, in this instance numbering four. As before, overpressure exhaust valves 56 may be provided to control the pressure within the exhaust chambers i5.

Additional molded orifice plates or interrupting heads 86 can be added to provide orifices as may be required.

Effective interruption of charging current is obtained by the delayed action in starting the air blast caused by the temporary plugging action of the contacts i5, it, which pull out the orifices l3, It only after adequate contact gap has been attained to avoid restriking at the next current zero. The advantages of such delayed action in fluid blast interrupters are set forth in U. S. patent application, filed December 15, 1943, S. N. 514,366, now U. S. Patent 2,592,635, issued April 15, 1952 to Winthrop M. Leeds, Robert E. Friedrich and Francis J. Fry, and assigned to the assignee of the instant application. The valve-controlled pressure maintained on the exhaust side of the orifices contributes importantly to the high dielectric strength built up between the contacts.

The above two embodiments of my invention disclose how, with the use of a single pair of movable contacts, I have provided an improved compressed-gas circuit interrupter employing novel features as heretofore pointed out. Using the arrangement of the modified interrupting heads of Figs. 3 and 4 additional orifices are obtained without increasing the number of contact rods employed. It will also be noted that with the construction of Figure 3 I have again employed the controlled pressure exhaust chamber '35 to increase the dielectric strength of the arcing region. It will also be noted that in both constructions disclosed the arrangement is simple, easy to inspect and maintain, and sturdy and rigid in constructional aspects. By the delayed action of the air blast, charging-current interruption without restriking is facilitated.

Although I have shown and described two embodiments of my invention, it is to be clearly understood that changes and modifications may readily be made therein by those skilled in the art, without departing from the spirit and scope of the appended claims.

I claim as my invention:

1. A compressed gas circuit interrupter including a pair of spaced insulating fiuid conducting columns, an interrupting fluid conducting head secured to each column, the two interrupting heads being disposed adjacent one another, enclosing means positioned between the interrupting heads and solely fastened thereto defining a substantially enclosed exhaust chamber, a movable contact associated with each interrupting head, the two movable contacts being movable apart during the opening operation to establish arcing, and the two columns and heads conducting opposed fluid blasts into the exhaust chamber to effect arc extinction.

2. A compressed gas circuit interrupter including a pair of spaced insulating columns, a tube secured adjacent the end of each column, an interrupting head mounted on one end of each tube, enclosing means positioned between the interrupting heads and fastened thereto defining a substantially enclosed exhaust chamber, a movable contact assembly disposed within each tube and including a movable contact, and removable fastening means holding the movable contact assembly in position, the movable contact assembly being movable out of the tube through the other end thereof without disturbing the two interrupting heads.

3. A compressed gas circuit interrupter including a pair of spaced insulating columns, a gas reservoir chamber disposed adjacent one end of each column, a tubular member secured to each reservoir chamber, an orifice-type interrupting head fastened to each tubular member through which compressed gas may flow for interrupting purposes, substantially enclosed exhaust chamber means positioned between the two heads and fastened thereto, and a movable contact assembly disposed within each tubular member.

a. A compressed gas circuit interrupter including a pair of spaced insulating columns, a gas reservoir chamber disposed adjacent one end or" each column, a tubular member secured to each reservoir, an interrupting head fastened to each tubular member adjacent one end thereof, substantially enclosed exhaust chamber means positioned between the two heads and fastened thereto, a movable contact assembly disposed within each tubular member, removable fastening means holding the movable contact assembly in position, the movable contact assembly movable out of the tubular member through the said other end thereof without disturbing the two interrupting heads or the exhaust chamber.

5. A compressed gas circuit interrupter including a pair of spaced orifice-type interrupting heads, an intermediately positioned interrupting head, a. pair of substantially enclosed exhaust chambers, each exhaust chamber being disposed between one interrupting head and an intermediately positioned interrupting head, fluid flow passage means interconnecting each interrupting head with an intermediately positioned interrupting head, a pressure chamber formed in the intermediately positioned interrupting head, a

plurality of orifices associated with the intermediately positioned interrupting head, an oriflce associated with each interrupting head, and movable rod-shaped contact means movable through the orifices.

6. A compressed gas circuit interrupter includ ing a pair of spaced insulating columns, an interrupting head secured to each column, the unsecured ends of the two interrupting heads facing each other, enclosing means positioned between the interrupting heads and fastened thereto defining a substantially enclosed exhaust chamber, at least one insulating column and its associated interrupting head transmitting a blast of compressed gas into the exhaust chamber during the interruption process, and overpressure valve means controlling the pressure within the substantially enclosed exhaust chamber.

7. A compressed gas circuit interrupter including a pair of spaced insulating columns, a gas reservoir chamber disposed adjacent one end of each column, an interrupting head secured to each gas reservoir chamber through which compressed gas may flow for interrupting purposes, and enclosing means positioned between the interrupting heads and fastened thereto defining a substantially enclosed exhaust chamber.

8. A compressed gas circuit interrupter including a pair of spaced insulating columns, a gas reservoir chamber disposed adjacent one end of each column, an interrupting head secured to each gas reservoir chamber, enclosing means positioned between the interrupting heads and fastened thereto defining a substantially enclosed exhaust chamber, and a movable contact assembly movable away from the interrupting head and through the gas reservoir chamber for inspection purposes.

9. A compressed gas circuit interrupter including a pair of spaced insulating columns, an oriflee-type interrupting head secured to each column, the two orifice-type interrupting heads facing each other, enclosing means positioned between the interrupting heads and fastened thereto defining a substantially enclosed exhaust chamber, a fluid motor disposed adjacent the end of each column, a rod-shaped movable contact associated with each orifice-type interrupting head and actuated by its respective fluid motor, and means biasing the two contacts toward the closed position.

10. A compressed gas circuit interrupter including a pair of spaced insulating columns, a tube secured adjacent the end of each column, an orifice-type interrupting head mounted on one end of each tube, enclosing means positioned between the interrupting heads and fastened thereto defining a substantially enclosed exhaust chamber, a fluid motor disposed adjacent the end of each column, a rod-shaped movable contact associated with each orifice-type interrupting head and actuated by its respective fluid motor, and means biasing the two contacts toward the closed position.

11. A compressed gas circuit interrupter including a pair of spaced insulating columns, at least one of the columns transmitting a blast of fluid, an interrupting head secured to each column and extending substantially transversely of the axial length thereof, the two interrupting heads being positioned adjacent one another, enclosing means positioned between the interrupting heads and solely fastened thereto defining a substantially enclosed exhaust chamber, a movable contact associated with at least one interrupting head and movable therein away from the other interrupting head during the opening operation to establish arcing, the interrupting head associated with said one fluid transmitting column providing a fluid conducting path from said column to the region adjacent the arcing to eifect arc extinction.

12. A compressed gas circuit interrupter including a pair of spaced insulating fluid transmitting columns, a fluid conducting interrupting head secured to each column and extending substantially transversely of the axial length thereof, the two interrupting heads being positioned adjacent one another, enclosing means positioned between the interrupting heads and solely fastened thereto defining a substantially enclosed exhaust chamber, a movable contact associated with each interrupting head and movable therein away from the other interrupting head during the opening operation to establish arcing, and the two columns and heads conducting opposed fluid blasts into the exhaust chamber to efiect arc extinction.

WINTHROP M. LEEDS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,895,907 Baum Jan. 31, 1933 1,965,551 Kopeliowitsch July 3, 1934 2,303,825 Cox Dec. 1, 1942 2,449,518 Strom Sept. 14, 1948 FOREIGN PATENTS Number Country Date 517,622 Great Britain Feb. 5, 1 40 

